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  1. 01 Sep, 2017 1 commit
  3. 31 Aug, 2017 9 commits
    • Paolo Valente's avatar
      doc, block, bfq: better describe how to properly configure bfq · 2670cd16
      Paolo Valente authored 
      Many users have reported the lack of an HOWTO for properly configuring
bfq as a function of the goal one wants to achieve (max
responsiveness, max throughput, ...). In fact, all needed details are
already provided in the documentation file bfq-iosched.txt. Yet the
document lacks guidance on which parameter descriptions to look
at. This commit adds some simple direction.
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Reviewed-by: default avatarJeremy Hickman <jeremywh7@gmail.com>
Reviewed-by: default avatarLaurentiu Nicola <lnicola@dend.ro>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      2670cd16
    • Paolo Valente's avatar
      doc, block, bfq: fix some typos and remove stale stuff · 233f0bf4
      Paolo Valente authored 
      In addition to containing some typos and stale sentences, the file
bfq-iosched.txt still mentioned a set of sysfs parameters that have
been removed from this version of bfq. This commit fixes all these
issues.
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Reviewed-by: default avatarJeremy Hickman <jeremywh7@gmail.com>
Reviewed-by: default avatarLaurentiu Nicola <lnicola@dend.ro>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      233f0bf4
    • Omar Sandoval's avatar
      loop: fold loop_switch() into callers · 43cade80
      Omar Sandoval authored 
      The comments here are really outdated, and blk-mq made flushing much
simpler, so just fold the two cases into the callers.
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      43cade80
    • Omar Sandoval's avatar
      loop: add ioctl for changing logical block size · 89e4fdec
      Omar Sandoval authored 
      This is a different approach from the first attempt in f2c6df7d
("loop: support 4k physical blocksize"). Rather than extending
LOOP_{GET,SET}_STATUS, add a separate ioctl just for setting the block
size.
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      89e4fdec
    • Omar Sandoval's avatar
      loop: set physical block size to PAGE_SIZE · 6c6b6f28
      Omar Sandoval authored 
      The physical block size is "the lowest possible sector size that the
hardware can operate on without reverting to read-modify-write
operations" (from the comment on blk_queue_physical_block_size()). Since
loop does buffered I/O on the backing file by default, the RMW unit is a
page. This isn't the case for direct I/O mode, but let's keep it simple.
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      6c6b6f28
    • Omar Sandoval's avatar
      loop: get rid of lo_blocksize · 8a0740c4
      Omar Sandoval authored 
      This is only used for setting the soft block size on the struct
block_device once and then never used again.
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      8a0740c4
    • Paolo Valente's avatar
      block, bfq: guarantee update_next_in_service always returns an eligible entity · 24d90bb2
      Paolo Valente authored 
      If the function bfq_update_next_in_service is invoked as a consequence
of the activation or requeueing of an entity, say E, then it doesn't
invoke bfq_lookup_next_entity to get the next-in-service entity. In
contrast, it follows a shorter path: if E happens to be eligible (see
commit "bfq-sq-mq: make lookup_next_entity push up vtime on
expirations" for details on eligibility) and to have a lower virtual
finish time than the current candidate as next-in-service entity, then
E directly becomes the next-in-service entity. Unfortunately, there is
a corner case for which this shorter path makes
bfq_update_next_in_service choose a non eligible entity: it occurs if
both E and the current next-in-service entity happen to be non
eligible when bfq_update_next_in_service is invoked. In this case, E
is not set as next-in-service, and, since bfq_lookup_next_entity is
not invoked, the state of the parent entity is not updated so as to
end up with an eligible entity as the proper next-in-service entity.

In this respect, next-in-service is actually allowed to be non
eligible while some queue is in service: since no system-virtual-time
push-up can be performed in that case (see again commit "bfq-sq-mq:
make lookup_next_entity push up vtime on expirations" for details),
next-in-service is chosen, speculatively, as a function of the
possible value that the system virtual time may get after a push
up. But the correctness of the schedule breaks if next-in-service is
still a non eligible entity when it is time to set in service the next
entity. Unfortunately, this may happen in the above corner case.

This commit fixes this problem by making bfq_update_next_in_service
invoke bfq_lookup_next_entity not only if the above shorter path
cannot be taken, but also if the shorter path is taken but fails to
yield an eligible next-in-service entity.
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Tested-by: default avatarLee Tibbert <lee.tibbert@gmail.com>
Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      24d90bb2
    • Paolo Valente's avatar
      block, bfq: remove direct switch to an entity in higher class · a02195ce
      Paolo Valente authored 
      If the function bfq_update_next_in_service is invoked as a consequence
of the activation or requeueing of an entity, say E, and finds out
that E belongs to a higher-priority class than that of the current
next-in-service entity, then it sets next_in_service directly to
E. But this may lead to anomalous schedules, because E may happen not
be eligible for service, because its virtual start time is higher than
the system virtual time for its service tree.

This commit addresses this issue by simply removing this direct
switch.
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Tested-by: default avatarLee Tibbert <lee.tibbert@gmail.com>
Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      a02195ce
    • Paolo Valente's avatar
      block, bfq: make lookup_next_entity push up vtime on expirations · 80294c3b
      Paolo Valente authored 
      To provide a very smooth service, bfq starts to serve a bfq_queue
only if the queue is 'eligible', i.e., if the same queue would
have started to be served in the ideal, perfectly fair system that
bfq simulates internally. This is obtained by associating each
queue with a virtual start time, and by computing a special system
virtual time quantity: a queue is eligible only if the system
virtual time has reached the virtual start time of the
queue. Finally, bfq guarantees that, when a new queue must be set
in service, there is always at least one eligible entity for each
active parent entity in the scheduler. To provide this guarantee,
the function __bfq_lookup_next_entity pushes up, for each parent
entity on which it is invoked, the system virtual time to the
minimum among the virtual start times of the entities in the
active tree for the parent entity (more precisely, the push up
occurs if the system virtual time happens to be lower than all
such virtual start times).

There is however a circumstance in which __bfq_lookup_next_entity
cannot push up the system virtual time for a parent entity, even
if the system virtual time is lower than the virtual start times
of all the child entities in the active tree. It happens if one of
the child entities is in service. In fact, in such a case, there
is already an eligible entity, the in-service one, even if it may
not be not present in the active tree (because in-service entities
may be removed from the active tree).

Unfortunately, in the last re-design of the
hierarchical-scheduling engine, the reset of the pointer to the
in-service entity for a given parent entity--reset to be done as a
consequence of the expiration of the in-service entity--always
happens after the function __bfq_lookup_next_entity has been
invoked. This causes the function to think that there is still an
entity in service for the parent entity, and then that the system
virtual time cannot be pushed up, even if actually such a
no-more-in-service entity has already been properly reinserted
into the active tree (or in some other tree if no more
active). Yet, the system virtual time *had* to be pushed up, to be
ready to correctly choose the next queue to serve. Because of the
lack of this push up, bfq may wrongly set in service a queue that
had been speculatively pre-computed as the possible
next-in-service queue, but that would no more be the one to serve
after the expiration and the reinsertion into the active trees of
the previously in-service entities.

This commit addresses this issue by making
__bfq_lookup_next_entity properly push up the system virtual time
if an expiration is occurring.
Signed-off-by: default avatarPaolo Valente <paolo.valente@linaro.org>
Tested-by: default avatarLee Tibbert <lee.tibbert@gmail.com>
Tested-by: default avatarOleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      80294c3b
  5. 29 Aug, 2017 6 commits
  7. 28 Aug, 2017 24 commits
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